Eliminate unnecessary restriction for unownedExecutor to main actor definition

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -4439,9 +4439,6 @@ ERROR(distributed_actor_protocol_illegal_inheritance,none,
 ERROR(broken_distributed_actor_requirement,none,
       "DistributedActor protocol is broken: unexpected requirement", ())
 
-ERROR(unowned_executor_outside_actor,none,
-      "'unownedExecutor' can only be implemented within the main "
-      "definition of an actor", ())
 ERROR(override_implicit_unowned_executor,none,
       "cannot override an actor's 'unownedExecutor' property that wasn't "
       "explicitly defined", ())

lib/Sema/TypeCheckProtocol.cpp

@@ -4948,19 +4948,6 @@ void ConformanceChecker::resolveValueWitnesses() {
         return;
       }
 
-      // Ensure that Actor.unownedExecutor is implemented within the
-      // actor class itself.  But if this somehow resolves to the
-      // requirement, ignore it.
-      if (requirement->getName().isSimpleName(C.Id_unownedExecutor) &&
-          Proto->isSpecificProtocol(KnownProtocolKind::Actor) &&
-          DC != witness->getDeclContext() &&
-          !isa<ProtocolDecl>(witness->getDeclContext()) &&
-          Adoptee->getClassOrBoundGenericClass() &&
-          Adoptee->getClassOrBoundGenericClass()->isActor()) {
-        witness->diagnose(diag::unowned_executor_outside_actor);
-        return;
-      }
-
       // Objective-C checking for @objc requirements.
       if (requirement->isObjC() &&
           requirement->getName() == witness->getName() &&